Find a course and run it
Jagex introduced six marked Agility stations across Ashenfall in update 0.12.1. Interact with a station’s flags, follow its fixed trail of orbs and try to improve your time. Courses can be repeated for XP. Rewards include medals, and mastering a regional course grants a decorated version of that region’s cape.
Build XP while traveling
Running around the world also gives passive Agility XP. Riding a mount does not give that passive XP. If you want to train as you move between objectives, travel on foot when it is practical; use a mount when travel speed matters more than incidental Agility training.
As the skill develops, sprinting uses less stamina. Jagex also lists higher-level increases to carry weight, safer falls and shortcuts through Kebbit Burrows. The burrows can be marked on the in-game map, but low-level attempts may cause damage, so avoid treating every shortcut as harmless.
Later movement tools
The update describes an aerial dash, a second jump and Recall, a skill spell that returns you to a placed runic marker. Windstep became an Agility spell in this update. These abilities change exploration and combat movement, but the release notes do not turn them into a single mandatory unlock order for every character.
If you are following an older movement guide, check the 0.12.1 date. The region index gives a broader picture of the world without claiming that the representative screenshot above depicts an Agility course.